Before the crew boards the aircraft for a commercial airline flight, is there anyone who checks the instruments and avionics system? I'm sure the engines are checked but what about the avionics systems, instruments, sensors,etc.?
There was an accident due to an incorrect reading of the pitot sensor, is there somebody to check it?
When pilots arrive to an aircraft for the first flight of the day, extra checks are performed by the crew to verify aircraft systems are all working properly. These checks are done once per day and subsequent flights will perform abbreviated checks instead. A visual walk around inspection is accomplished before and after every flight.
Maintenance will check on airplanes at required intervals but outside of specific checks (associated with the carriers approved maintenance program) the only time they'll check something like a pitot tube is if the crew notes a problem and writes it up. At that point maintenance will address the issue to return the aircraft to airworthiness.
Before crew board the aircraft for a commercial airline, is there any person who checks the instruments and avionics systems
In between flights there is no check of Pitot tube operation from the cockpit prior to crew arrival.
There was an accident due to incorrect reading of pico sensor
There have been a few accidents where one pitot tube (not pico sensor) was blocked (e.g. by the actions of a mud dauber wasp). This can lead to inconsistent readings in the two pilot's displays and/or with data fed to an autopilot.
In theory the pilot in command (the Captain) has responsibility for making sure everything works before flight. On small aircraft responsible pilots always check all instruments and sensors. For example, a pitot tube will be checked to make sure that it is clear and that no spider or mud wasp has taken up residence therein. Another key check is to make sure the antennas are all there and firmly attached. Most checklists have at bare minimum an "instruments" line item and may have many line items for specific instruments. When a pilot does the "walk around" they will specifically examine each and every external sensor such as static ports, etc.
Unfortunately, commercial pilots rarely have time to do such thorough checks, which can be very time consuming for a large aircraft. In many cases they will often not even do a walk around, even if their airline's policy mandates it.